People have skills, and skills come from training and experience. Recent graduates often have a clearer memory of specific aspects of their training. If I needed to have someone implement a customized hash table, chances are I'd seek out someone who had recently been to college or to a training program that focused on algorithms. That does not mean I would look for a "junior"; some "juniors" are self-taught. Some had education that focused less on fundamentals and more on a specific tech stack.